A semiconductor device having a triple-well can achieve a higher speed operation due to the fact that its back gate voltage can be reduced and parasitic capacitance can be reduced by, for example, optimizing a bias state of a p-type well and an n-type well. Formation of such a triple well structure normally includes multiple ion implantation steps and heat treatment steps, which amount to a large number of steps, and therefore the reduction of these steps is desired.
An object of the present invention is to reduce the number of steps in manufacturing a triple-well that includes multiple ion implantation steps and heat treatment steps.